Smog-Cutting Concrete

The new Interstate 35W bridge in Minneapolis includes two 30-foot-tall sculptures made of photocatalytic concrete. Though the squiggly sculptures are supposed to invoke the international symbol for water, they use a combination of sunlight and titanium dioxide to do their air-scrubbing.

The best (industry-offered) explanation of how this process works can be found here; the gist is that titanium dioxide (a common white pigment, used in everything from cream cheese to paint) embedded in the concrete acts as a catalyst for the polluting chemicals, breaking them down faster than ultraviolet light alone. Nowhere is the anti-pollution benefit of the sculptures quantified, however: But even if a couple of giant Ionic Breeze machines would work better, the sculptures are an important investment in a passive technology that until now has been used mainly in (gasp) France.